Nutrients from surrounding topsoil are made available to the rose plant through its hair-like feeder roots. Topsoil is the upper 2 to 8 inches of soil. Roses and all plants need 17 nutrients to grow and thrive, all of them in the topsoil. Digging around rose bush topsoil disturbs its feeder roots and its ability to absorb nutrients.
A rose bush's deep anchor roots hold it in place in the soil. Many rose bush varieties live for hundreds of years and have very deep anchor roots. Good nutrition from feeder roots near the surface is an important component to long-lived rose plants. Anchor roots are kept healthy with deep watering once a week. Feeder roots must be fed from the surrounding soil.
Roses thrive with a soil renewal program. Nutrients are replaced in topsoil by adding organic matter and organic amendments. Compost improves soil structure and adds the 17 nutrients that roses need to thrive. Compost can be easily made in a backyard compost bin and does not need to be dug in around a rose bush. Layering it on the soil surface allows slow absorption of nutrients.
Rose bushes are strong and vigorous when provided with a slow, steady supply of nutrients from composted soil. There is no need to dig it in around the bush. The microorganism population that creates nutrients is enhanced and supported by organic compost. Over 4 billion microorganisms live in 1 teaspoon of healthy soil. Soil becomes self-sustaining over time when organic compost is added regularly for the microorganisms to feed on.